Flame retardant flexibilized polyphenylene ether compositions

ABSTRACT

There are provided flame retardant, flexibilized thermoplastic compositions which comprise, in admixture, a normally flammable polyphenylene ether resin, an aromatic phosphate plasticizer in an amount at least sufficient to provide a flame retardant, flexibilized composition after molding, and a thermoplastic elastomer comprising a block copolymer of a vinyl aromatic compound and a diene monomer. Preferred features comprise such compositions which also include a halogenated hydrocarbon, alumina trihydrate and/or elemental red phosphorus.

This is a divisional of application Ser. No. 08/306,219, filed on Sep.14, 1994, now abandoned, which is a continuation of Ser. No. 08/053,981,filed on Apr. 27, 1993, now abandoned, which is a divisional of Ser. No.07/118,525, filed on Nov. 9, 1987, now U.S. Pat. No. 5,206,276, which isa continuation of Ser. No. 06/948,233, filed on Dec. 31, 1986, nowabandoned, which is a continuation of Ser. No. 06/603,663, filed Apr.26, 1984, now U.S. Pat. No. 4,684,682, which is a continuation of Ser.No. 06/197,933, filed on Oct. 17, 1980, now abandoned, which is acontinuation of Ser. No. 05/752,731, filed on Dec. 21, 1976, nowabandoned.

The present invention relates to flame retardant, flexibilizedthermoplastic polyphenylene ether compositions. The compositions of thisinvention comprise the polyphenylene ether, an aromatic phosphate and athermoplastic elastomer such as A-B-A¹ block copolymers, e.g.,polystyrene-polybutadiene-polystyrene, and optionally, a halogenatedhydrocarbon resin, alumina trihydrate and/or elemental red phosphorus.

BACKGROUND OF THE ART

The polyphenylene ether resins are well known in the art as a class ofthermoplastics which possess a number of outstanding physicalproperties. They can be prepared, in general, by oxidative andnon-oxidative methods, such as are disclosed, for example, in Hay, U.S.Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff, U.S. Pat. Nos.3,257,357 and 3,257,358, which are incorporated herein by reference.

In is known that the polyphenylene ether resins alone are somewhatdifficult to fabricate because of their high temperature thermoplasticmolding characteristics and this has limited their use in applicationswhere flexibility, such as the need to calendar into relatively thinsheets, without cracking or crazing, is desirable.

In recent years, there has also been increasing concern about theperformance and safety of thermoplastic materials, including theafore-mentioned polyphenylene ether compositions during real-life firesituation.

Of particular interest would be a polyphenylene ether composition whichis both flexibilized and flame retardant without loss of desirableproperties.

It is known that flexible polyphenylene ether blends have been made withfairly high loadings of plasticizers. It has now been found that thecapabilities and alternatives in making such blends can be greatlyexpanded by incorporating rubber in the form of a block copolymer intosuch blends, and further that if the flexibilizer is predominately anaromatic phosphate, good self-extinguishing properties are obtained.

Based on the foregoing discovery, it has also been found possible tofurther modify the blends to make them somewhat less costly, withoutloss of other beneficial properties, by replacing some of the aromaticphosphate with a halogenated hydrocarbon resin, e.g., chlorinatedparaffin. Complete replacement of the aromatic phosphate is notpossible, however, without loss of flame resistance.

Furthermore, based on the foregoing discovery, it has also been foundpossible to decrease the cost of the formulation, without introducing ahalogen source, and at the same time, improve the self-extinguishingproperties. This discovery comprises including alumina trihydrate in thecomposition.

Finally, based on the foregoing discovery, it has also been foundpossible to use higher levels of thermoplastic elastomer withoutdisrupting flame retardant properties and still keeping a halogen-freesystem by the addition to the composition of elemental red phosphorus.

In addition to being useful by themselves, the new compositions areuseful in blends with other resins and elastomers to improve flameretardancy. Of course, conventional additives such as pigments, fillers,stabilizers, and the like, can be used with the new compositions of thisinvention.

DESCRIPTION OF THE INVENTION

Accordingly, the present invention provides in its broadest aspects, aflame retardant flexibilized thermoplastic composition which comprises,in admixture:

(a) a normally flammable polyphenylene ether resin;

(b) a flame retardant aromatic phosphate plasticizer in an amount atleast sufficient to provide a flexibilized composition after molding;and

(c) a thermoplastic elastomer comprising an A-B-A¹ block copolymerwherein terminal blocks A and A¹ are polymeric units of a vinyl aromaticcompound and center block B is a polymer of a conjugated diene.

As employed herein, the term "flexibilized" is used in itsart-recognized sense to define compositions which are calenderable intorelatively thin sheets, e.g., 1/4 inch or less in thickness, which canbe bent without causing cracking or crazing. Such thermoplasticcompositions are suitable, in appropriately thin forms, for productssuch as shower curtains wall coverings, automotive upholstery, and thelike.

The ten "normally flammable" as used herein, describes compositionswhich do not meet the V-0 and V-1 requirements of the Underwriters'Laboratories Bulletin No. 94 test.

In a preferred feature, the new compositions will also include:

(d) a minor proportion of flame retardant halogenated plasticizer basedon the amount of aromatic phosphate component (b) . Especially preferredhalogenated hydrocarbons are chlorinated paraffins. The amount can vary,but up to equal parts by weight, 50:50, based on the aromatic phosphateare preferred, and 50:50 is most economical. A useful chlorinatedparaffin is available from ICI America, Inc., under the designationCreclor S-45.

Another preferred feature is the new composition which also includes:

(e) a minor proportion of alumina trihydrate, sufficient to enhance theflame retardant capability of aromatic phosphate component (b) . Theamount can vary widely within these limits but preferably, the amount ofalumina trihydrate (which is a standard item of commerce), comprisesfrom about 5 to about 40 parts by weight per 100 parts by weight ofcomponents (a) and (b) combined.

Still another preferred feature is the new composition which alsoincludes:

(f) a minor proportion of elemental red phosphorus, sufficient toenhance the flame retardant capability of aromatic phosphate component(b). Elemental red phosphorus can be used in fairly broad ranges inamount but preferably, it will comprise from about 1 to about 10 partsby weight per 100 parts by weight of components (a), (b) and (c)combined.

The normally flammable polyphenylene ether resin (a) is preferably ofthe type having the structural formula: ##STR1## wherein the oxygenether atom of one unit is connected to the benzene nucleus of the nextadjoining unit, n is a positive integer and is at lease 50, and each Qis a monovalent substituent selected from the group consisting ofhydrogen, halogen, hydrocarbon radicals free of a tertiary alpha-carbonatom, halohydrocarbon radicals having at least two carbon atoms betweenthe halogen atom and the phenyl nucleus, hydrocarbonoxy radicals andhalohydrocarbonoxy radicals having at least two carbon atoms between thehalogen atom and the phenyl nucleus.

A more preferred class of polyphenylene ether resins for thecompositions of this invention includes those of the above formulawherein each Q is alkyl, most preferably, having from 1 to 4 carbonatoms. Illustratively, members of this class includepoly(2,6-dimethyl-1,4-phonylone)ether; poly-(2,6-diethyl-1,4-phenylene)ether; poly(2-methyl-6-ethyl--1,4phenylene)ether;poly(2-methyl-6-propyl-1,4-phenylene)ether;poly(2,6-dipropyl-1,4-phonylone)ether;poly(2-ethyl-6-propyl-1,4-phenylene)ether; and the like.

Especially preferred is poly(2,6-dimethyl-1,4phenylene)ether,preferably, having an intrinsic viscosity of about 0.45 deciliters pergram (dl./g.) as measured in chloroform at 30° C.

The choice of an aromatic phosphate plasticizer can vary broadly.

The phosphate plasticizer is preferably a compound of the formula:##STR2## wherein R¹, R² and R³ are the same or different and are aryl,alkyl substituted aryl, or hydroxyalkyl. To keep the amount of halogenlow, it is preferred that no halogen be present in component (b).

Examples include cresyl diphenyl phosphate, tricresyl phosphate,triiosopropylphenyl phosphate, tripheny phosphate, cresyl diphenylphosphate, or mixtures thereof. Especially preferred is triphenylphosphate.

Commercially available aromatic phosphates which have been found to beparticularly useful are FMC Corporations's Kronitex 50 and Kronitex 300,which are isopropylated triphenyl phosphate compounds.

The plasticizer (b) is added in amounts which will be sufficient toprovide a flexibilized composition within the meaning of the termdescribed above. In general, the plasticizer is present in amountsranging from at least about 10 to 100, preferably from about 15 to about65 parts by weight of plasticizer, per 100 parts of resin component (a).

The present compositions also include thermoplastic elastomers (c),which are A-B-C¹ block copolymers. In general, these resins comprise apolymerized center block B which is derived from a conjugated diene,e.g., butadiene, isoprene, 1,3-pentadiene, and the like, and polymerizedterminal blocks A and A¹ which are derived from vinyl aromatic, e.g.,styrene compounds, such as styrene, α-methyl styrene, vinyl toluene,vinyl xylene, vinyl naphthalene, and the like. Preferably, the A-B-A¹block copolymer will have terminal blocks A and A¹ comprised ofpolystyrene and a center block comprised of polybutadiene.

The linear A-B-A¹ block copolymers are made by an organometallicinitiated polymerization process using, for example, sodium or lithiummetal or an organic derivative thereof. The diene monomers can bepolymerized with a monofunctional or difunctional initiator, as isdescribed in Kennedy et al, Interscience Publishers, Vol. 23, Part II(1969), pages 553-449. Other methods of preparing these block copolymersare described in Zelinski, U.S. Pat. No. 3,251,905 and Holden et al,U.S. Pat. No. 3,231,635, the disclosures of which are incorporatedherein by reference to save unnecessary detail.

Commercially available A-B-A¹ block copolymers include Kraton X4119,poly(styrene-butadiene-styrene) with 20% mineral oil, and the Kratonsdesignated as K-1101 (polystyrene-polybutadiene-polystyrene), K-1102(polystyrene-polybutadiene-polystyrene), and K-1107(polystyrene-polyisoprene-polystyrene), all from Shell Chemical Company,Polymers Division.

Hydrogenated A-B-A¹ block copolymers can also be used as thermoplasticelastomers in the present compositions. These are prepared by techniqueswhich are well known in the art. See, for instance, the disclosure inJones, U.S. Pat. No. 3,431,323, which is incorporated herein byreference. A preferred commercially available copolymer of this type isShell Chemical's KG-6521 resin.

The thermoplastic elastomer (c) can vary broadly in amount, butgenerally is present in amounts from about 10 to about 100, morepreferably from about 15 to about 55 parts by weight of thermoplasticelastomer per 100 parts of polyphenylene ether (a).

Other ingredients, such as fillers, reinforcements, pigments,stabilizers, lubricants, and the like, may be added for theirconventional purposes.

The manner in which the present compositions are prepared is notcritical and conventional methods can be employed. Preferably, however,each of the ingredients is added as part of a blend premix, and thelatter is passed through an extruder, e.g., a 28 mm. WP twin screwextruder, at an extrusion temperature of from about 350° to about 550°F., dependent on the needs of the particular composition. The strandsemerging from the extruder may be cooled, chopped into pellets, andmolded or calendered to any desired shape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples are illustrative of the compositions of thisinvention. They are not intended to limit the invention in any manner.

EXAMPLES 1-10

The following blends were prepared in a 28 mm Werner Pfleiderer twinscrew extruder and tested for physical properties and flame retardancyby the Underwriters' Laboratory U.L. 94 test and the GE Oxygen IndexTest, with results set forth in Table 1:

                                      TABLE 1                                     __________________________________________________________________________    Flexibilized Polyphenylene Styrene Compositions Comprising                    Aromatic Phosphates and A--B--A.sup.1 Block Copolymers                        Example           A.sup.a                                                                           1   2   3   4   5   6   7   8   9    10                 __________________________________________________________________________    Composition (parts by weight)                                                 (a)                                                                             poly(2,6-dimethyl-1,4-                                                                        60  60  60  60  60  60  60  55  55  55   55                   phenylene)ether                                                             (b)                                                                             aromatic phosphate.sup.b                                                                      --  --  --  --  --  --  --  45  45  45   45                   aromatic phosphate.sup.c                                                                      40  40  40  40  40  40  40  --  --  --   --                 (c)                                                                             thermoplastic elastomer block                                                                 --  20  40  60  80  100 --  25  --  --   --                   copoly(styrene-butadiene-                                                     styrene).sup.d                                                                block copoly(styrene-butadiene                                                                --  --  --  --  --  --  100 --  25  --   --                   styrene).sup.e                                                                block copoly(styrene-isoprene-                                                                --  --  --  --  --  --  --  --  --  25   --                   styrene).sup.f                                                                hydrogenated block copoly-                                                                    --  --  --  --  --  --  --  --  --  --   25                   (styrene-butadiene styrene).sup.g                                           Properties                                                                    Tensile yield, psi                                                                              6300                                                                              3700                                                                              3000                                                                              2100                                                                              2000                                                                              1800                                                                              700 2000                                                                              1300                                                                              1600 1500               Elongation, %     66  60  71  74  51  59  135 65  67  71   77                 U.L. flame self-extinguishing                                                                   1/drip                                                                            1/1 10/10                                                                             12/24                                                                             35/15                                                                             drip                                                                              drip                                                                              1/2 1/4 1/3  2/3                times, sec./sec.                                                              Oxygen index. %   --  --  --  --  --  --  --  34  31  31   31.5               __________________________________________________________________________     .sup.a Control Experiment                                                     .sup.b FMC's Kronitex 50                                                      .sup.c FMC's Kronitex 300                                                     .sup.d Shell Chemical's Kraton 1101                                           .sup.e Shell Kraton 1102                                                      .sup.f Shell Kraton 1107                                                      .sup.g Shell Kraton G6521                                                

It is of particular interest to note that in the above flexible blendswhich contain an aromatic phosphate as the plasticizer, goodself-extinguishing properties are obtained. Thus, the presentcompositions, particularly those containing between 20 and 80 parts byweight of A-B-A¹ block copolymer per 100 parts by weight ofpolyphenylene ether and aromatic phosphate, are flame retardant withoutthe chance to produce toxic and corrosive halogen-derived products oninciteration.

EXAMPLES 11 and 12

Following the procedure of Examples 1-10, the listed compositions areprepared, having the properties set forth in Table 2:

                  TABLE 2                                                         ______________________________________                                        Compositions Comprising Polyphenylene Ethers, Aromatic                        Phosphates, A--B--A.sup.1 Block Copolymer                                     and Halogenated Hydrocarbon Resin                                             Example            11.sup.a                                                                              12      B.sup.e                                    ______________________________________                                        Composition(parts by weight)                                                  (a) poly(2,6-dimethyl-1,4-                                                                           60      60    60                                           phenylene)ether                                                           (b) aromatic phosphate.sup.a                                                                         40      20    --                                       (c) thermoplastic elastomer block                                                                    43      43    43                                           copoly(styrene-butadiene-                                                     styrene).sup.b                                                            (d) chlorinated paraffin.sup.d                                                                       --      20    40                                       Properties                                                                    Tensile yield, psi 1700    2200    2000                                       Elongation, %      70      156     160                                        U.L. flame self-extinguishing                                                                    19/24   28/26   41 drips                                   times, sec./sec.                   flaming                                                                       resin                                      Oxygen index, %    32      30.5    21                                         ______________________________________                                         .sup.a Control Experiment in the sense that all flame retardancy is           conferred by aromatic phosphate (b).                                          .sup.b FMC's aromatic phosphate Kronitex 50, which is an isopropylated        triphenyl phosphate.                                                          .sup.c Shell Chemical's Kraton 1102.                                          .sup.d ICI America Inc.'s Creclor S45, which is a chlorinated paraffin.       .sup.e Control Experiment                                                

It is noteworthy that in these compositions, complete replacement of thearomatic phosphate by chlorinated paraffin is catastrophic to the flameresistance, whereas up to 50% replacement is only slightly detrimental.

EXAMPLES 13-15

Following the procedure of Examples 1-10, the listed compositions areprepared, having the properties set forth in Table 3:

                  TABLE 3                                                         ______________________________________                                        Compositions Comprising Polyphenylene Ethers, Aromatic                        Phosphates A--B--A.sup.1 Block Copolymer and Alumina Trihydrate               Example          11.sup.a                                                                              13      14    15                                     ______________________________________                                        Composition(parts by weight)                                                  (a) poly(2,6-dimethyl-1,4--                                                                        60      60    60    60                                       phenylene)ether                                                           (b) aromatic phosphate.sup.b                                                                       40      40    40    40                                   (c) thermoplastic elastomer                                                                        43      43    43    43                                       block copoly(styrene-                                                         butadiene styrene).sup.c                                                  (d) alumina trihydrate                                                                             --      10    20    30                                   Properties                                                                    Tensile yield, psi                                                                             1700    2000    1700  1700                                   Elongation, %    70      53      57    51                                     U.L. flame self-extinguishing                                                                  19/24   11/11   3/11  2/6                                    times, sec./sec.                                                              Oxygen index, %  32      29      30    31                                     ______________________________________                                         .sup.a Control Experiment in the sense that no alumina trihydrate is used     .sup.b FMC's aromatic phosphate Kronitex 50, which is an isopropylated        triphenyl phosphate                                                           .sup.c Shell Chemical's Kraton 1102.                                     

It is seen that the properties can be retained with significant costadvantages by addition of alumina trihydrate.

EXAMPLES 16-17

Following the procedure of Examples 1-10, the listed compositions areprepared, having the properties set forth in Table 4:

                  TABLE 4                                                         ______________________________________                                        Compositions Comprising Polyphenylene Ethers, Aromatic                        Phosphates, A--B--A.sup.1 Block Copolymer and                                 Elemental Red Phosphorus                                                      Example             C.sup.a  16      17                                       ______________________________________                                        Composition(parts by weight)                                                  (a) poly(2,6-dimethyl-1,4--                                                                           30       30    30                                         phenylene)ether                                                           (b) aromatic phosphate.sup.b                                                                          30       30    30                                     (c) thermoplastic elastomer                                                                           40       40    40                                         block copoly(styrene-butadiene-                                               styrene).sup.c                                                            (d) elemental red phosphorus                                                                          --       2     5                                      Properties                                                                    Tensile strength, psi                                                                             1700     1700    1600                                     Elongation, %       106      127     126                                      U.L. flame self-extinguishing                                                                     18/25    4/4     1/8                                      time, sec./sec.                                                               ______________________________________                                         .sup.a Control Experiment in the sense that no elemental red phosphorus i     present.                                                                      .sup.b FMC's aromatic phosphate Kronitex 50, which is an isopropylated        triphenyl phosphate.                                                          .sup.c Shell Chemical's Kraton 1102.                                     

It is seen that red phosphorus permits the incorporation of high amountsof rubber, while maintaining good flame retardant characteristics. Thesecompositions also have the desirable feature of being free of halogen.

Obviously, other modifications and variations of the present inventionare possible in the light of the above description. It is, therefore, tobe understood that changes may be made in the particular embodimentsdisclosed herein which are within the full intended scope of theinvention as defined in the appended claims.

I claim:
 1. A flame retardant, flexibilized thermoplastic compositionhaving a tensile yield less that about 3700 psi which comprises, inadmixture:(a) a normally flammable polyphenylene ether resin; (b) 65 to100 parts by weight of a flame retardant aromatic phosphate plasticizerbased upon 100 parts by weight of (a); and (c) 15 to 65 parts by weightof a thermoplastic elastomer, based upon 100 parts by weight of (a),comprising an A-B-A¹ block copolymer wherein terminal blocks A and A¹are polymeric units of a vinyl aromatic compound and center block B is apolymer of a conjugated diene and wherein said A-B-A¹ block copolymer isa hydrogenated A-B-A¹ block copolymer.
 2. The composition as defined inclaim 1 wherein the polyphenylene ether resin (a) has the formula:##STR3## wherein the oxygen ether atom of one unit is connected to thebenzene nucleus of the next adjoining unit n is a positive integer andis at least 50 and each Q is a monovalent substituent selected from thegroup consisting of hydrogen, halogen, hydrocarbon radicals free of atertiary alpha-carbon atom, halohydrocarbon radicals andhalohydrocarbonoxy radicals having at least two carbon atoms between thehalogen atom and the phenyl nucleus.
 3. The composition as defined inclaim 2 wherein the polyphenylene ether resin (a) ispoly(2,6-dimethyl-1,4-phenylene)ether.
 4. The composition as defined inclaim 1 wherein the flame retardant aromatic phosphate plasticizer (b)is a compound of the formula: ##STR4## wherein R¹, R² and R³ are thesame or different and are aryl, alkyl substituted aryl, or hydroxyaryl.5. The composition as defined in claim 4 wherein the flame retardantaromatic phosphate plasticizer (b) is selected form the group consistingof cresyl diphenyl phosphate, tricresyl phosphate, triisopropylphenylphosphate, triphenyl phosphate, cresyl diphenyl phosphate and mixturesthereof.
 6. The composition as defined in claim 5 wherein the flameretardant aromatic phosphate plasticizer (b) is triisopropylphenylphosphate.
 7. The composition as defined in claim 1 wherein terminalblocks A and A1 are derived from vinyl aromatics selected from the groupconsisting of styrene, alpha-methyl styrene, vinyl toluene, vinyl xyleneand vinyl naphthalene and wherein center lock B is derived fromconjugated diene selected from the group consisting of butadiene,isoprene and 1,3-pentadiene.
 8. The composition as defined in claim 1 inwhich component (c) is present in an amount of from about 20 to about 80parts by weight.
 9. The composition as defined in claim 8 in whichcomponent (c) is present in an amount of from about 20 to about 25 partsby weight.
 10. A flame retardant, flexibilized thermoplastic compositionhaving a tensile yield less that about 3700 psi consisting of, inadmixture:(a) a normally flammable polyphenylene ether resin; (b) 65 to100 parts by weight of a flame retardant aromatic phosphate plasticizerbased upon 100 parts by weight of (a); and (c) 15 to 65 parts by weightof a thermoplastic elastomer, based upon 100 parts by weight of (a),comprising and A-B-A¹ block copolymer wherein terminal blocks A and A¹are polymeric units of a vinyl aromatic compound and center block B is apolymer of a conjugated diene and wherein said A-B-A¹ block copolymer isa hydrogenated A-B-A¹ block copolymer.
 11. The composition as defined inclaim 10 in which component (c) is present in an amount of from about 20to about 80 parts by weight.
 12. A composition as defined in claim 11 inwhich component (c) is present in an amount of from about 20 to about 25parts by weight.